The present invention relates to a portable telephone apparatus, and in particular, to a portable telephone apparatus for use in a portable telephone system and provided with at least two antennas.
A mobile communication system using a portable telephone set or the like has been rapidly developed in recent years. In general, a radio wave received by a mobile communication system is a multiple waves including a direct wave from a wave source and reflected waves from obstacles present in midway paths. In this case, the receiving sensitivity deteriorates due to fading. Therefore, a digital portable telephone system or the like performs diversity receiving in order to reduce the fading.
FIG. 19 is a block diagram showing a structure of a conventional portable telephone apparatus, and FIG. 20 is a perspective view showing an analysis model for simulating the portable telephone apparatus shown in FIG. 19.
Referring to FIG. 19, a whip antenna 202 of an external antenna extending upward from a feeding point 203 is provided on the top portion of the housing 201 of the portable telephone apparatus, the feeding point 203 of the whip antenna 202 is connected with a radio transmitter circuit 205 provided with a microphone 306 through a feeding cable 209 and the contact xe2x80x9caxe2x80x9d of a transmitting and receiving switch 204, and is connected with a receiving diversity circuit 207 through the feeding cable 209 and the contact xe2x80x9cbxe2x80x9d of the transmitting and receiving switch 204. A planar inverted-F antenna 206 of an internal antenna built in the housing 201 and a radio receiver circuit 208 provided with a speaker 305 are connected with the receiving diversity circuit 207.
Referring to FIG. 20, a speaker 212 close to an ear of a human body of a user is provided on an upper portion of a front surface 201a of the portable telephone apparatus, and a microphone 211 close to a mouth of the human body is provided on a lower portion of the front surface 201a. Moreover, the whip antenna 202 is provided in the vicinity of one of four corners on a top surface of the housing 201 located at the upper portion of the speaker 212.
On the other hand, the planar inverted-F antenna 206 is provided in the housing 201 at an upper portion of a rear surface 201b which opposes to the front surface 201a. It is noted that since FIG. 20 shows an analysis model for simulation, the planar inverted-F antenna 206 is located outside of the rear surface 201b of the housing 201, however, in the case of an actual portable telephone apparatus, the planar inverted-F antenna 206 is provided so as to be located inside of the rear surface 201b of the housing 201. This planar inverted-F antenna 206 is constituted by comprising a rectangular conductor plate 206 supported by a feeding pin 206 so as to be parallel to the rear surface of the housing 201, a central portion of the upper side of the conductor plate 206 is connected with the receiving diversity circuit 207 illustrated in FIG. 19 through the feeding pin 206, and the central portion of the conductor plate 206 is grounded through a short-circuit pin 206c. 
In the portable telephone apparatus constituted as described above, the transmitting and receiving switch 204 is switched over to the contact xe2x80x9caxe2x80x9d side by a controller (not shown) of the portable telephone apparatus upon transmitting, and at this time, a radio signal modulated in accordance with an audio signal inputted to a microphone 306 is fed by being outputted to the whip antenna 202 from the radio transmitter circuit 205 through the transmitting and receiving switch 204. On the other hand, upon receiving, the transmitting and receiving switch 204 is switched over to the contact xe2x80x9cbxe2x80x9d side by the controller, and at this time, a radio signal received by the whip antenna 202 is inputted to the receiving diversity circuit 207 through the contact xe2x80x9cbxe2x80x9d of the transmitting and receiving switch 204, and a radio signal received by the planer inverted-F antenna 206 is inputted to the receiving diversity circuit 207. The receiving diversity circuit 207 selects a radio signal having a higher level out of the radio signal received by the whip antenna 202 and the radio signal received by the planar inverted-F antenna 206, and outputs the selected radio signal to the radio receiver circuit 208. Thereafter, the radio receiver circuit 208 demodulates the received radio signal so as to generate and output an audio signal from the speaker 305.
As described above, in the above-mentioned portable telephone apparatus, a radio signal having a higher level is selected out of signals received by two antennas 202 and 206 upon receiving, and only the whip antenna 202 is used upon transmitting.
In the analysis model of FIG. 20, the housing 201 had a rectangular-parallelepiped shape of 125 mm height, 35 mm width, and 20 mm depth, and at this time, the feeding point 203 of the whip antenna 202 was set to an origin of an XYZ coordinate system, and the longitudinal direction of the whip antenna 202 was set to the Z-axis direction. In this case, -X direction is a direction parallel to an audio (or voice)-radiating direction from the speaker 212, and is a direction directed to the head of a human body, in particular, to an ear of the human body. X direction is a direction opposite to the audio-radiating direction from the speaker 212.
FIGS. 21, 22, and 23 show radiating directivities on X-Y plane, X-Z plane, and Y-Z plane, respectively, in a free space of radio waves transmitted from the portable telephone apparatus shown in FIGS. 19 and 20.
In the above-mentioned simulation, a radiating directivity when exciting the whip antenna 202 by inputting a radio signal to the feeding point 203 was obtained by analyzing the directivity by the publicly-known moment method. In this case, the frequency of radio signals was set to 900 MHz, the housing 201, the whip antenna 202 and the planar inverted-F antenna 203 were each made of an electrical conductor, and the analysis model was equivalently replaced with a wire grid in order to reduce the calculation time to perform a simulation (for example, See Prior art document 1 of Koichi Ogawa et al., xe2x80x9cAn Error Rate Performance of a xcfx80/4-shift QPSK Signal for a Handset Diversity Influenced by Head and Shoulder Effectsxe2x80x9d, Technical Report of IEICE (Institute of Electronics, Information and Communication Engineers in Japan), A-P 99-110, RC 88-107, October 1999xe2x80x9d).
As apparent from FIGS. 21 to 23, it is found that the xcex8-directional component Excex8 of the electric field on X-Y plane is almost omni-directional.
As described above, for example, the whip antenna 202 or the like is used as an external antenna of a portable telephone apparatus, however, it is preferable that the directivity of the antenna 202 is isotropic (omni-directional on the horizontal plane) so as to be able to receive even a signal transmitted from any direction upon waiting for reception. However, since the whip antenna 202 exists adjacent to the speaker 212, the directivity thereof is influenced by the human body such as an ear or a head thereof so that the directivity thereof deteriorates. Moreover, in this case, radio wave absorption by the head has been a large problem.
FIG. 24 is a side view showing a structure of a human body model carrying the portable telephone apparatus shown in FIGS. 19 and 20, and FIG. 25 is a front view showing a structure of a human body model carrying the portable telephone apparatus shown in FIGS. 19 and 20.
Referring to FIGS. 24 and 25, the human body model for simulation is constituted by comprising a head portion 302, a left shoulder portion 303 and a hand portion 304 in order to take into consideration the influence of the shoulder of the human body onto the radiating directivity of the antenna, and a half-length model constituted by integrating the head portion and the left shoulder portion is used as the human body model. In this case, the head 302 is approximated to a cylindrical shape having a diameter of 180 mm and a height of 250 mm, and the left shoulder 302 is approximated to a shape of trapezoidal column. In this case, in the left shoulder portion 303, the longitudinal section in the front and back direction of the human body is in a shape of trapezoidal. Moreover, the hand portion 304 of the human body model carrying the portable telephone apparatus has a shape of U-character having a thickness of 20 mm and a height of 80 mm, which is separated from the side surface of the housing 201 and the conductor plate 206 of the planar inverted-F antenna 203 by keeping an interval of 10 mm, and the hand portion 304 is provided so as to cover a lower portion of the housing 201. Moreover, on the assumption that the ear is located at the center P of the side surface of the head portion 302, the portable telephone apparatus is provided in such a state that it can be rotated about the center P of the side surface so that an interval between the head portion 302 and the housing 201 is set to 2 cm and the tilt angle of the longitudinal direction of the portable telephone apparatus from the vertical direction becomes 60 degrees. In this case, on the assumption that the portions 302, 303, and 304 of the human body model have a relative dielectric constant of 42, respectively, the human body model is equivalently replaced with a wire grid in order to reduce the calculation time to perform a simulation and obtain the radiating directivity when exciting the whip antenna 202 by inputting a radio signal to the feeding point 203 through analysis by the publicly-known moment method.
FIGS. 26, 27 and 28 are views showing radiating directivities transmitted from the portable telephone apparatus shown in FIGS. 19 and 20 when the potable telephone apparatus is carried by the human body model shown in FIGS. 24 and 25 on X-Y plane, X-Z plane, and Y-Z plane.
As apparent from comparing the results of FIGS. 26 to 28 with the results of FIGS. 21 to 23, it is found that the radiation pattern of the portable telephone apparatus when approaching to the human body is smaller than that in the case of the free space, and the radiating directivity deteriorates. From the above simulation, it was found that the loss of the power inputted to the whip antenna 202 due to the head portion 302 of the human body model became 18.3%, the loss of the power due to the left shoulder portion 303 of the human body model became 1.9%, the loss of the power due to the hand portion 304 of the human body model became 0.3%, and thus the loss of the power due to the head portion 302 of the human-body model accounts for approximately 20% of the total loss.
Moreover, the mean effective gain (MEG) Ge in the above case was calculated. The mean effective gain Ge is obtained by formulating the effective gain of an antenna moving in a multiple wave propagation path and is described as shown below in Prior art document 2 of Koichi Ogawa et al., xe2x80x9cMean Effective Gain Analysis of a Diversity Antenna for Portable Telephone in Mobile Communication Environmentsxe2x80x9d, IEICE (Institute of Electronics, Information and Communication Engineers in Japan) Transaction, Vol. J81-B-II, No. 10, pp. 897-905, October 1998.
That is, the mean effective gain Ge is represented by the following Equation:                     Ge        =                              P            rec                                              P              1                        +                          P              2                                                                    (          1          )                ,            
where Prec denotes the mean receiving power of the antenna, P1 denotes the mean receiving power in the multiple wave propagation path of the antenna having an isotropic directivity for a xcex8-component polarized wave, and P2 denotes the mean receiving power in the multiple wave propagation path of an antenna having the isotropic directivity for a xcfx86-component polarized wave. Therefore, P1+P2 denotes the total of incoming wave powers in the space in which the antenna is provided. The mean receiving power Prec is obtained in Prior art document 3 of W. C. Jakes, xe2x80x9cMicrowave Mobile Communicationsxe2x80x9d, pp. 133-140, IEEE Press, 1974xe2x80x3, and it is represented by the following equation:                               P          rec                =                              ∫            0                          2              ⁢                              xe2x80x83                            ⁢              π                                ⁢                                    ∫              0              π                        ⁢                                          {                                                                            P                      1                                        ⁢                                                                  G                        θ                                            ⁡                                              (                        Ω                        )                                                              ⁢                                                                  P                        θ                                            ⁡                                              (                        Ω                        )                                                                              +                                                            P                      2                                        ⁢                                                                  G                        φ                                            ⁡                                              (                        Ω                        )                                                              ⁢                                                                  P                        φ                                            ⁡                                              (                        Ω                        )                                                                                            }                            ⁢                              ⅆ                Ω                                                                                  (          2          )                ,            
where xcexa9 denotes a coordinate point (xcex8, xcfx86) in a spherical coordinate system, and d xcexa9=sinxcex8dxcex8dxcfx86. Gxcex8(xcexa9) and Gxcfx86 (xcexa9) denote a xcex8 component and xcfx86 component of the power gain directivity of the antenna, respectively. Moreover, Pxcex8(xcexa9) and Pxcfx86(xcexa9) denote angle density functions for the xcex8 component and the xcfx86 component of the incoming wave to the antenna. When defining the ratio of mean receiving powers received by the antenna having the isotropic directivity for the vertical (xcex8) and horizontal (xcfx86) polarized waves as a cross polarization power ratio XPR, which is represented by the following equation:                     XPR        =                              P            1                                P            2                                                        (          3          )                .            
The mean effective gain Ge is represented by the following equation (4) from the above equations (3) to (5) (for example, See Prior art document 4 of T. Taga, xe2x80x9cAnalysis for mean effective gain of mobile antennas in land mobile radio environmentsxe2x80x9d, IEEE Transaction, Vol. VT-39, No. 2, pp. 117-131, 1990):                     Ge        =                              ∫            0                          2              ⁢                              xe2x80x83                            ⁢              π                                ⁢                                    ∫              0              π                        ⁢                                          [                                                                            XPR                                              1                        +                        XPR                                                              ⁢                                                                  G                        θ                                            ⁡                                              (                        Ω                        )                                                              ⁢                                                                  P                        θ                                            ⁡                                              (                        Ω                        )                                                                              +                                                            1                                              1                        +                        XPR                                                              ⁢                                                                  G                        φ                                            ⁡                                              (                        Ω                        )                                                              ⁢                                                                  P                        φ                                            ⁡                                              (                        Ω                        )                                                                                            ]                            ⁢                              ⅆ                Ω                                                                                  (          4          )                ,            
where Gxcex8(xcexa9) and Gxcfx86(xcexa9) were obtained in accordance with the above-described wire grid model. Moreover, Pxcex8(xcexa9) and Pxcfx86(xcexa9) were given by the following equations on the assumption that vertical and horizontal polarized wave components of the incoming wave were uniformly distributed in the azimuth direction and were Gauss-distributed in the elevation angle direction:                               P          θ                =                              A            θ                    ⁢                      exp            [                          -                                                                    {                                          θ                      -                                              (                                                                              π                            2                                                    -                                                      m                            V                                                                          )                                                              }                                    2                                                  2                  ⁢                                      xe2x80x83                                    ⁢                                      σ                    V                    2                                                                        ]                    ⁢                      xe2x80x83                    ⁢          and                                              (          5          )                ,                                          P          φ                =                              A            φ                    ⁢                      exp            [                          -                                                                    {                                          θ                      -                                              (                                                                              π                            2                                                    -                                                      m                            H                                                                          )                                                              }                                    2                                                  2                  ⁢                                      xe2x80x83                                    ⁢                                      σ                    H                    2                                                                        ]                                                        (          6          )                ,            
where Axcex8 and Axcfx86 denote proportional constants, mV and mH denote mean elevation angles of respective polarized wave distributions of xcex8 and xcfx86, respectively, and "sgr"V and "sgr"H denote standard deviations of respective polarized wave components of xcex8 and xcfx86.
The mean effective gain Ge defined as described above was calculated using the above Equation (4) when making the portable telephone apparatus approach to the above human body model. In this case, on the assumption that the cross polarization power ratio XPR is equal to 6 (typical value in urban area), vertical and horizontal polarized wave components of the incoming wave are uniformly distributed in the azimuth direction, and elevation angles are Gauss-distributed in the direction of 30 degrees (it is generally known that elevation angles exist in a range from 0 to 40 degrees) with a standard deviation of 20 degrees, then the mean effective gain Ge in the radiating directivities shown in FIGS. 26 to 28 becomes xe2x88x924.6 dBi which is comparatively small.
A first object of the present invention solves the above-mentioned problems, and is to provide a portable telephone apparatus provided with at least two antennas and a control method thereof, each of which is capable of reducing the radiation of radio signals in the audio radiating direction from the speaker.
Further, a second object of the present invention solves the above-mentioned problems and is to provide a portable telephone apparatus provided with at least two antennas and a control method thereof, each of which is capable of controlling a portable telephone apparatus so that the mean effective gain Ge can be further increased as compared with that in the case of the prior art.
In order to dissolve the above-mentioned problems, a portable telephone apparatus according to the present invention is characterized by comprising transmitting means for transmitting radio signals by simultaneously exciting at least two antennas with a predetermined amplitude ratio and a predetermined phase difference so that a main beam of a radiation pattern has a direction substantially opposite to an audio radiating direction from a speaker.
In the above-mentioned portable telephone apparatus, the transmitting means preferably transmits the radio signals by simultaneously exciting the respective antennas with a predetermined amplitude ratio and a predetermined phase difference so that an mean effective gain becomes larger than that when exciting one antenna.
Also, in the above-mentioned portable telephone apparatus, the transmitting means preferably excites the respective antennas only for transmission of telephone speech.
Further, the above-mentioned portable telephone apparatus preferably further comprises receiving means for receiving radio signals by using the at least two antennas, and selectively receiving a radio signal having the highest level among the radio signals received by the antennas, using a diversity receiving system.
Furthermore, in the above-mentioned portable telephone apparatus, the at least two antennas preferably include an external antenna provided outside of a housing of the portable telephone apparatus, and an internal antenna built in the housing of the portable telephone apparatus.
In the above-mentioned portable telephone apparatus, the external antenna is a half-wave whip antenna, and the internal antenna is a planar inverted-F antenna. In this case, the external antenna is constituted by a whip antenna and a helical antenna which are mechanically joined with each other so as to be electrically insulated from each other,
wherein the helical antenna is connected with a radio circuit of the portable telephone apparatus when the external antenna is housed in the housing of the portable telephone apparatus, while the whip antenna is connected with the radio circuit of the potable telephone apparatus when the external antenna is extended,
wherein the potable telephone apparatus further comprises detecting means for detecting whether or not the external antenna is housed in the housing of the portable telephone apparatus, and
wherein the transmitting means simultaneously excites the external antenna and the internal antenna with the predetermined amplitude ratio and the predetermined phase difference so that the main beam of the radiation pattern has the direction substantially opposite to the audio radiating direction from the speaker when it is detected by the detecting means that the external antenna is housed in the housing of the portable telephone apparatus, while the transmitting means excites only the external antenna when it is detected by the detecting means that the external antenna is not housed in the housing of the portable telephone apparatus.
Also, in the above-mentioned portable telephone apparatus, the transmitting means excites the at least two antennas with phases opposite to each other.
Further, in the above-mentioned portable telephone apparatus, the above-mentioned at least two antennas preferably include two quarter-wave antennas. Otherwise, the above-mentioned at least two antennas preferably include two half-wave antennas. Alternatively, in the above-mentioned potable telephone apparatus, preferably, the above-mentioned at least two antennas are internal antennas built in the housing of the portable telephone apparatus.
A control method of a telephone apparatus according to the present invention is characterized by including a step of:
transmitting and controlling so as to transmit radio signals by simultaneously exciting at least two antennas with a predetermined amplitude ratio and a predetermined phase difference so that a main beam of a radiation pattern has a direction substantially opposite to an audio radiating direction from a speaker.
In the above-mentioned control method of the telephone apparatus, the step of transmitting and controlling preferably transmits the radio signals by simultaneously exciting the respective antennas with a predetermined amplitude ratio and a predetermined phase difference so that an mean effective gain becomes larger than that when exciting one antenna.
Accordingly, the present invention makes it possible to realize a radiating directivity for strongly radiating radio waves in the direction opposite to a head of a human body of a user, so that deterioration of the radiating directivity of the antenna can be reduced when making a portable telephone apparatus approach to the human body. Moreover, it is possible to realize the radiating directivity of the antenna suitable for a multi-path waves propagation environment.